Yoke and pinion angle

I have a 71 convertible cutlass supreme, 2004r, 391 gears.
My questions are; how in the lamest terms possible do you adjust pinion angle? Also I have the car sitting higher with a lift kit, roughly 3 inches higher and the yoke at the trans is coming out a little over an inch? Is that much to be worried about or do I need a longer shaft? Don't know how much is tolerable? If I could straighten this out maybe I could enjoy my car

Depth of your yoke is fine.
You have an automatic car so 2-3 degrees down angle is good.
I can't envision how raising the body effects pinion angle, in other words I'm not sure if that raises the nose of the diff, or not but that would be important. Not to the overall equation because you still want 2-3* down angle. So if raising your vehicle raised or lowered the vehicle you would have to compensate.

Depth of your yoke is fine.
You have an automatic car so 2-3 degrees down angle is good.
I can't envision how raising the body effects pinion angle, in other words I'm not sure if that raises the nose of the diff, or not but that would be important. Not to the overall equation because you still want 2-3* down angle. So if raising your vehicle raised or lowered the vehicle you would have to compensate.

Ok, let me elaborate. I've put 'lift cups' under the springs. Front about 3 inches and back about 2 inches and I have fully adjustable rear arms - top and bottom. Problem is upper adjustables are 2 inches longer than original stock and when I lower the car I notice my yoke coming out. It's not a super high lift by any means but my angles need some correcting which will take some patients.
When you say 2-3 down angle what does that mean? How do you measure?

Ok, let me elaborate. I've put 'lift cups' under the springs. Front about 3 inches and back about 2 inches and I have fully adjustable rear arms - top and bottom. Problem is upper adjustables are 2 inches longer than original stock and when I lower the car I notice my yoke coming out. It's not a super high lift by any means but my angles need some correcting which will take some patients.
When you say 2-3 down angle what does that mean? How do you measure?

If I am visualizing this correctly, raising the body/frame would change the driveshaft angles. This would be downward at the front yoke and upward at the rear U-joint.
"Upper ajustables" ? Are you referring to upper control arms ? If so, being 2" longer than original, that would change the angles differently. You would be raising the front of the differential higher from the ground and decreasing the angle at the rear U-joint and probably decreasing the angle at the front yoke.
I may be wrong on this, so let some others chime in.

The yoke is going to slide in or out of the transmission depending on the difference in height of the frame vs the differential at some point. It will also change depending on the length of the control arms.

Your upper control arms should be the same length as stock. Since you have a 71 did you exchange 64-67 uppers for what you had? Those would be 2.5 inches longer than the 68-72. Not something you want to do.

Pinion angle is the angle of the pinion gear in the differential in relation to the ground. Level would be 0 degrees, in other words, parallel to the ground. For a stock car that might be 1-3 degrees down angle which means the nose of the diff is pointing downward toward the ground, up angle would be pointing up toward the body. With two inch longer upper control arms the top of your diff would be rolled backward 2.5 inches which would raise the nose up in the air toward the body. Not a good thing.
It's measured with an angle gauge, here's an example.

Your upper control arms should be the same length as stock. Since you have a 71 did you exchange 64-67 uppers for what you had? Those would be 2.5 inches longer than the 68-72. Not something you want to do.

Pinion angle is the angle of the pinion gear in the differential in relation to the ground. Level would be 0 degrees, in other words, parallel to the ground. For a stock car that might be 1-3 degrees down angle which means the nose of the diff is pointing downward toward the ground, up angle would be pointing up toward the body. With two inch longer upper control arms the top of your diff would be rolled backward 2.5 inches which would raise the nose up in the air toward the body. Not a good thing.
It's measured with an angle gauge, here's an example.

I'm using the lift kit that was made for 68-72 cutlass. Now that I look at the upper arms I'm just going to adjust those all the way back in. Its still 2 inches longer than stock but I think with a little over an inch of yoke sticking out it'll be alright. I'm going to work on getting this angle right and see where I'm at from there. Thanks for the help guys

Ok, You never going to get this right if know one knows how to get it done...lol.

The pinion angle only matters to the driveline angle...THAT IS IT. NOT to the ground.

Now what is correct for your car...??? We can not tell you. You need to find the pinion angle from the transmission output shaft the slip yoke u-joint will give you that. turn the u-joint so it is facing the ground you will need angle finders
the rear end yoke should be in the same u-joint cup position as the front (phased in) measure that angle you should be able to subtract one from the other and come up with a positive or negative number. which will be your running drive line angle.

Now there are books out there and google search es to help with this

To adjust the tail shaft you can add shim under your trans mount or subtract with a shorter trans mount
BUT the easiest way is to use upper adjustable control arms to adjust your rear pinion angle to get the correct running drive line angle needed to stop oscillation or vibration.

So even if you have the car on a hill this all will still be the same as long as the wheels are flat on the ground or on a drive on lift.

YOU CAN NOT jack the car up and let the rear hang...THIS will not give you correct measuring.